What's New

First Look Plant Disease article January 2016

First Report of Phytophthora cinnamomi Causing Root Rot of Castanea mollissima (Chinese chestnut) in China.

Chengzhong Lan, Hongchun Ruan, and Jinai Yao


3-year-old plants of Castanea mollissima were found with leaf discolouration, wilting, and stunted growth associated with severe root rot in several commercial nurseries in Jianou, Fujian, China. Five Phytophthora-like isolates were isolated from necrotic taproots and identified as Phytophthora cinnamomi on the basis of morphological characteristics and molecular analyses. Pathogenicity tests were carried out and Koch's postulates were fulfilled. This is the first report of Phytophthora root rot of C.mollissima caused by P. cinnamomi in China.

New Phytopathology article January 2016

Host Phenology and Leaf Effects on Susceptibility of California Bay Laurel to Phytophthora ramorum

Steven F.Johnston, Michael F.Cohen, TamasTorok, Ross K.Meentemeyer, and Nathan E.Rank
January 2016, Volume 106, Number 1. Pages 47-55. http://dx.doi.org/10.1094/PHYTO-01-15-0016-R
Spread of the plant pathogen Phytophthora ramorum, causal agent of the forest disease sudden oak death, is driven by a few competent hosts that support spore production from foliar lesions. The relationship between traits of a principal foliar host, California bay laurel (Umbellularia californica), and susceptibility to P. ramorum infection were investigated with multiple P. ramorum isolates and leaves collected from multiple trees in leaf-droplet assays. We examined whether susceptibility varies with season, leaf age, or inoculum position. Bay laurel susceptibility was highest during spring and summer and lowest in winter. Older leaves (>1 year) were more susceptible than younger ones (8 to 11 months). Susceptibility was greater at leaf tips and edges than the middle of the leaf. Leaf surfaces wiped with 70% ethanol were more susceptible to P. ramorum infection than untreated leaf surfaces. Our results indicate that seasonal changes in susceptibility of U. californica significantly influence P. ramorum infection levels. Thus, in addition to environmental variables such as temperature and moisture, variability in host plant susceptibility contributes to disease establishment of P. ramorum.


New Mycologia article

The Phytophthora species assemblage and diversity in riparian alder ecosystems of western Oregon, US.

LL Sims, W. Sutton, P. Reeser, and EM. Hansen. 2015. Mcologia 7:105 pp. 889 - 902 http://www.mycologia.org/cgi/doi/10.3852/14-255


Phytophthora species were systematically sampled, isolated, identified and compared for presence in streams, soil and roots of alder (Alnus species) dominated riparian ecosystems in western Oregon. We describe the species assemblage and evaluate Phytophthora diversity associated with alder. We recovered 1250 isolates of 20 Phytophthora species. Only three species were recovered from all substrates (streams, soil, alder roots): P. gonapodyides, the informally described “P. taxon Pgchlamydo”, and P. siskiyouensis. P. alni ssp. uniformis along with five other species not previously recovered in Oregon forests are included in the assemblage: P.citricola s.l., P. gregata, P. gallica, P. nicotianae and P. parsiana. Phytophthora species diversity was greatest in down- stream riparian locations. There was no significant difference in species diversity comparing soil and unwashed roots (the rhizosphere) to stream water. There was a difference between the predominating species from the rhizosphere compared to stream water. The most numerous species was the informally described “P. taxon Oaksoil”, which was mainly recovered from, and most predominant in, stream water. The most common species from riparian forest soils and alder root systems was P. gonapodyides.

New Genomics Data article

Genome sequences of six Phytophthora species associated with forests in New Zealand

D.J. Studholme, R.L. McDougal, C. Sambles, E. Hansen, G. Hardy, M. Grant, R.J. Ganley and N.M. Williams. 2016. Genomics Data Vol. 7, pp 54-56.



In New Zealand there has been a long association of Phytophthora diseases in forests, nurseries, remnant plantings and horticultural crops. However, new Phytophthora diseases of trees have recently emerged. Genome sequencing has been performed for 12 Phytophthora isolates, from six species: Phytophthora pluvialis, Phytophthora kernoviae, Phytophthora cinnamomi, Phytophthora agathidicida, Phytophthora multivora and Phytophthora taxon Totara. These sequences will enable comparative analyses to identify potential virulence strategies and ultimately facilitate better control strategies. This Whole Genome Shotgun data have been deposited in DDBJ/ENA/GenBank under the accession numbers LGTT00000000, LGTU00000000, JPWV00000000, JPWU00000000, LGSK00000000, LGSJ00000000, LGTR00000000, LGTS00000000, LGSM00000000, LGSL00000000, LGSO00000000, and LGSN00000000.


Leaf ‘bait’ uncovers dieback crossbreeds

ScienceNetwork Western Australia, Wednesday, 16 September 2015 article by Samille Mitchell

  • Dieback becomes pathogenic as it mixes with other species
  • South-west waterway ‘fishing’ reveals naturally occurring hybrid
  • Discovery raises questions about how species came into contact

MURDOCH University scientists have discovered the first known natural occurrence of hybrids of the plant pathogen Phytophthora, commonly known as the dieback, which has ravaged south-west bushland and forests.

But the Centre of Phytophthora Science and Management (CPSM) research also shows that Phytophthora is not always the ‘baddy’ of the plant world that it is perceived to be.

Murdoch University Associate Professor Treena Burgess says Phytophthora species naturally occur in many areas throughout WA, and not all become damaging pathogens.

She says Phytophthora species tend to become more pathogenic the more they hybridise.

But she says the newly discovered natural hybrids come from relatively low-pathogenic parent species and therefore do not pose a big risk to native vegetation in the short-term.

She cites example of naturally occurring endemic species of Phytophthora in the northern sandplains which are believed to survive on plant roots with little impact.

However, if a seedling from its host plant sprouts nearby, the Phytophthora will kill it, thus ensuring wider spread growth for the host species.

“Everything that’s naturally occurring is here for a reason,” she says.

“Everything is interconnected—we just don’t see what’s going on underneath the earth.”

Before this discovery Phytophthora hybrids had only been known from mixing in nurseries, rather than from the natural environment.



New Phytopathology article

Winter Conditions Correlate with Phytophthora alni Subspecies Distribution in Southern Sweden

Miguel A. Redondo, Johanna Boberg, Christer H. B. Olsson, and Jonàs Oliva

Phytopathology 2015 105:9, 1191-1197 http://dx.doi.org/10.1094/PHYTO-01-15-0020-R

During the last century, the number of forest pathogen invasions has increased substantially. Environmental variables can play a crucial role in determining the establishment of invasive species. The objective of the present work was to determine the correlation between winter climatic conditions and distribution of two subspecies of the invasive forest pathogen Phytophthora alni: P. alni subspp. alni and uniformis killing black alder (Alnus glutinosa) in southern Sweden. It is known from laboratory experiments that P. alni subsp. alni is more pathogenic than P. alni subsp. uniformis, and that P. alni subsp. alni is sensitive to low temperatures and long frost periods. By studying the distribution of these two subspecies at the northern limit of the host species, we could investigate whether winter conditions can affect the geographical distribution of P. alni subsp. alni spreading northward. Sixteen major river systems of southern Sweden were systematically surveyed and isolations were performed from active cankers. The distribution of the two studied subspecies was highly correlated with winter temperature and duration of periods with heavy frost. While P. alni subsp. uniformis covered the whole range of temperatures of the host, P. alni subsp. alni was recovered in areas subjected to milder winter temperatures and shorter frost periods. Our observations suggest that winter conditions can play an important role in limiting P. alni subsp. alni establishment in cold locations, thus affecting the distribution of the different subspecies of P. alni in boreal regions.


New Forest Pathology article

Action of fosetyl-al and metalaxyl against Phytophthora austrocedri

Silva, P. V., Vélez, M. L., Hernández Otaño, D., Nuñez, C., Greslebin, A. G. (2015). Forest Pathology. doi: 10.1111/efp.12216

Fosetyl-Al and metalaxyl, the most commonly used systemic fungicides against Phytophthora, were evaluated for their efficacy to control Phytophthora austrocedri, the pathogen that causes a serious disease at the Austrocedrus chilensis forests in Patagonia. The effect of the chemicals on pathogen development in vitro and in planta was analysed. Both chemicals were shown to protect plants from the pathogen. In vitro assays showed that asexual reproduction was sensitive to both chemicals. However, mycelial growth and sexual reproduction, which were clearly sensitive to metalaxyl, were sensitive only to high concentrations of fosetyl-Al. Fosetyl-Al and metalaxyl had almost the same efficacy when applied preventively by soil drench to seedlings. This difference between in vitro and in planta results can be attributed to the dual action of fosetyl-Al, not only inhibiting the pathogen but also stimulating host defence. In adult trees, preventive and curative treatments were tested, but only the fosetyl-Al preventive treatment was effective in the assayed conditions. Interestingly, seedlings pretreated with both fungicides were less susceptible to the effectors secreted by the pathogen. Our results indicate that fosetyl-Al and metalaxyl provide some resistance to the plant besides the fungistatic direct action on the pathogen. Further studies to elucidate a possible resistance-inducing activity of these chemicals and the mechanisms involved are underway.


New Plant Disease Note

First Report of Phytophthora occultans Causing Root and Collar Rot on Ceanothus, Boxwood, Rhododendron, and Other Hosts in Horticultural Nurseries in Oregon, USA

P. W.Reeser, W.Sutton, and E. M.Hansen, Department of Botany and Plant Pathology, Oregon State University, Corvallis OR 97331 USA; E. M.Goheen, USDA Forest Service, Forest Health Protection, Medford, OR USA; V. J.Fieland, Department of Botany and Plant Pathology, Oregon State University, Corvallis OR 97331 USA; and N. J.Grunwald, USDA-ARS, Horticultural Crops Research Lab, Corvallis OR 97331. http://dx.doi.org/10.1094/PDIS-02-15-0156-PDN

New Disease Reports

Phytophthora siskiyouensis causing stem lesions and cankers on Alnus incana

A. Perez-Sierra*, M. Kalantarzadeh, S. Sancisi-Frey and C.M. Brasier

New Disease Reports (2015) 31, 17. [http://dx.doi.org/10.5197/j.2044-0588.2015.031.017]

In late summer 2013, stem cankers and sparse foliage were reported on European grey alder (Alnus incana) growing on a 500 ha site recently-planted with broadleaf and coniferous trees in south-west England. A site visit showed that approximately 10% of  more than 1000 grey alders (thought to have been imported from Europe and planted in the late 1990s) had symptoms including bleeding stem lesions similar to those caused by Phytophthora alni (Gibbs et al., 2003). In November 2013, samples were collected from stem lesions (Fig. 1), roots (internal lesions tracking-down from stem lesions) and rhizosphere soil from symptom-bearing trees. Tissue from root and stem lesion margins was plated onto Phytophthora selective medium (SMA) (amended as per Brasier et al., 2005) and incubated at 20°C for 48 hrs. Green apples were used as baits for soil samples by inserting a few grams of soil under a flap cut in the side of the apple and incubating for 4-7 days at 20°C. Isolation from developing SMA mycelial cultures and incubated apple baits onto potato dextrose agar (PDA) and carrot agar (CA) was then undertaken.


Plant Disease - Disease Note

First Report of Phytophthora pluvialis Causing Needle Loss and Shoot Dieback on Douglas-fir in Oregon and New Zealand

E. M.Hansen, P.Reeser, and W.Sutton, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331; and J.Gardner and N.Williams, New Zealand Forest Research Institute (Scion), Private Bag 3020, Rotorua 3046, New Zealand.
May 2015, Volume 99, Number 5
Page 727